Studies are being pursued in the following areas: (1) on the mechanism of action of the enzyme, 2-keto-4-hydroxyglutarate aldolase, as obtained in pure form from extracts of either mammalian tissues or bacteria. This work includes an examination of the kinetics of the reaction catalyzed, a study of the properties of the tritium exchange half-reaction with pyruvate and also of the functional groups in the enzyme molecule involved in this catalytic process, and characterization of the subunit structure of this enzyme. (2) on the occurrence, validity, and properties of this coupled sequence of metabolic reactions, as catalyzed by enzymes in brain or bacteria; gamma- hydroxyglutamic acid yields CO2 plus alpha-hydroxy-gamma-aminobutyric acid yields malic acid semialdehyde yields malic acid. (3) on the purification, properties, and metabolic role of L-threonine dehydrogenase and a new D-1-amino-2-propanol: NAD plus oxidoreductase, which enzymes are found in extracts of animal tissues and bacteria.